The Skeneidae is a family with minute, umbilicate
shells usually 1-3 mm in size. It is of uncertain placement and extent,
and has been a
repository for assorted genera and species of small shells difficult to
place in other families. Some authors treat it a a separate family,
others as a subfamily of the Turbinidae, while others distribute the
included genera into other families. The animals are related to the
Trochidae but differ in the structure of
the ctenidium and in the arrangement of the tentacles, and the shells
differ by lacking an inner nacreous layer. For convenience it is treated
here as a family, while recognising that the placement and content are
not yet determined.

Shell form and sculpture is very variable in the Skeneidae, from planispiral to turbiniform, and from smooth to strongly
sculptured with axial and spiral ornamentation. The unifying features
are a thin and uncoloured shell, with a narrow to wide umbilicus often
sculptured with spiral ribs within, a circular aperture and a
multispiral corneous operculum. The protoconch appears smooth under the
light microscope, with a well-defined junction to the teleoconch.

The habitats of the Australian species are poorly
known. They are so small that specimens are usually sorted from beach
washup, algae and rock washings or dredge samples, without the actual
detail of habitat being clear. There is no documentation of gut
contents, diet or feeding behaviour.

In contrast to the lack of knowledge of most members
of the family, a group of deep water species found on waterlogged wood
was closely investigated by Marshall (1988). Wood from depths down to
1100 m from New Zealand and New South Wales was found to provide a
habitat, in the holes produced by boring bivalves, for a suite of minute
molluscs, including 18 new species of Skeneidae. Three of these species
occur in NSW waters and are included here.

The NSW species of Skeneidae were first revised by
Laseron (1954), as part of a heterogeneous grouping that he referred to
as Liotiidae. Over the following 55 years, observations on external
morphology and anatomy of the animals has lead to the distribution of
the species he treated into the Turbinidae, Vitrinellidae, Cornirostridae, Trochidae,
Orbitestillidae, and Omalogyridae, with 24 taxa allocated to
Skeneidae. Laseron based his work entirely on shell morphology, had a
limited range of specimens, and apparently did not have access to type
specimens from Tasmania, Victoria, and South Australia. Consequently he
assigned names to species which had already been named, particularly in
the genera Brookula and Liotella. Of the seven species of Brookula
he named, only one name is not in synonymy, and in Liotella none
of his names have survived. These synonyms are introduced as new in this
work, but most of them were recognised by Dr. W.F. Ponder who commenced,
but did not publish, a revision of the family in the 1980s.

There are 24 species referred to the family here.
All of them are considered endemic to Australia, but may well be found
to have wider distributions. Many are assigned distributions from NSW to
South Australia, including Tasmania, based on the collections of the
Australian Museum and the publication of May (1923) cataloguing the
Tasmanian fauna, and of Cotton (1959) cataloguing the South Australian
fauna. With further research the ranges of at least some will probably
be found to extend from southern Queensland to south-western WA, as is
the case for many other molluscs that occur in NSW.

Family References

Only the most important references for species
identification are given here. Other references cited in the text are
listed in "References", accessible from the "Table of
Contents" page.

Laseron, C.F. 1954. Revision of the Liotiidae of
New South Wales. Australian Zoologist 12: 1-25.

Marshall, B.A. 1988. Skeneidae, Vitrinellidae
and Orbitestellidae (Mollusca: Gastropoda) associated with biogenic
substrata from bathyal depths off New Zealand and New South Wales. Journal
of Natural History 22(4): 949-1004.

Coverage

All of the species from NSW that could be positively
identified and referred to this family have been included here. The
Australian Museum collection holds many specimens that may be undescribed species, and others that may be
forms of named species.
However, the common species from the intertidal zone and from shallow
water have been named and are covered here, allowing perhaps 90% of specimens collected
in these zones to be identified.

Identification Notes

With the exception of Crossea concinna,
shells in this family are less than 3 mm in size. They vary widely in form, but have in common a narrow to wide umbilicus, circular
aperture and are uncoloured. Shells that are similar in these characters
are found in the Trochidae, but are generally larger. Small species
generally similar in form are found in the Eatoniellidae, Vitrinellidae,
Rissoidae, Assimineidae, Elachisinidae, Cornirostridae and
Orbitestellidae.